The first sentence means he ceased to practice medicine 10 years ago. It is something that no longer happens. Because the time period mentioned has finished (the time period of medical practice) we could use the simple past tense and rephrase the above as:

"He practised medicine up to ten years ago."

The second sentence means that he began to practice medicine ten years ago and still continues to do so up to the present time. It is an unfinished activity so we can use the present perfect or even the present perfect continuous and rephrase it as:

He has practised medicine for ten years.

Or

He has been practising medicine for ten years.

The present perfect continuous merely emphasises the duration of the activity as if seeking to imply that he must be good at it because he practised it for so long or he was doing so diligently and professionally.